Abstract:Most of the high-performance all-polymer
solar cells (all-PSCs) reported to date are based on polymer donor and polymer
acceptor pairs with largely overlapped light absorption properties, which
seriously limits the efﬁciency of all-PSCs. This study reports the development of a series
of random copolymer donors possessing complementary light absorption with the
naphthalenediimide-based polymer acceptor P(NDI2HD-T2) for highly efﬁcient all-PSCs. By controlling the molar
ratio of the electron-rich benzodithiophene (BDTT) and electron-deﬁcient ﬂuorinated-thienothiophene (TT-F) units, a
series of polymer donors with BDTT:TT-F ratios of 1:1 (P1), 3:1 (P2), 5:1 (P3),
and 7:1 (P4) are prepared. The synthetic control of polymer composition allows
for precise tuning of the light absorption properties of these new polymer
donors, enabling optimization of light absorption properties to complement
those of the P(NDI2HD-T2) acceptor. Copolymer P1 is found to be the optimal
polymer donor for the fullerene-based solar cells due to its high light
absorption, whereas the highest power conversion efﬁciency of 6.81% is achieved for the
all-PSCs with P3, which has the most complementary light absorption with
P(NDI2HD-T2).